Bodies of water, and in particular those bodies of water that are recirculated, provide fertile breeding grounds for algae, bacteria, viruses, fungi, and other pathogens if the water is left untreated. Microbial contamination can create a variety of problems, ranging from aesthetic unpleasantries, such as slimy green water, to serious health risks such as fungal, bacterial, or viral infections.
Swimming pools and other recirculating bodies of water used for recreational purposes, such as hot tubs or spas, are particularly conducive to microbial growth, as users introduce new pathogens as they bathe or swim.
Ponds, such as garden or fish ponds, often desirably contain some microorganisms as nutrients for their inhabitants. In some circumstances, however, growth of undesirable and even desirable microorganisms can become uncontrolled, reducing the ability of the pond to support other desirable organisms by increasing the pond's biological oxygen demand or BOD. Industrial or agricultural ponds, used for storing water used in manufacturing or agricultural applications, are also subject to uncontrolled growth of microorganism that can form sufficient biomass to become entrained with the water and interfere with the operation of industrial or agricultural machinery or processes.
Recirculating water cooling systems, such as natural draft cooling towers, recycle heated cooling water by contacting the water with an unsaturated gas, such as air, thereby cooling the water by evaporation, and can also be used to cool the air, which may then be used to ventilate areas inhabited by humans or other animals. Microorganisms can be introduced by the cooling surfaces of the device, or by the air that comes into contact with the water. Their growth, if allowed to go unchecked, can result in sufficiently dense masses of organic material to clog or foul water flow lines and valves, contribute to rot or corrosion, and decrease cooling efficiency.
Similarly, humidification systems, where water is sprayed into warm, unsaturated air to cause essentially adiabatic mass transfer of some of the water to the air in the form of water vapor, can also result in transfer of pathogenic microorganisms from the water to the air. Since this humidified air is often intended for breathing by humans or other animals, the result can be infection by the contaminants transferred to the air from the water.
While many of these microbial contaminants that can grow in untreated water are harmless, others can be pathogenic and lead to outbreaks of infectious disease. One of the most common waterborne disease is dermatitis, which can be caused by an overgrowth of Pseudomonas aeruginosa bacteria. Other common diseases that can result from pathogens in bathing or swimming water include bacterial gastroenteritis, external otitis (swimmer's ear), candidia and tinea pedis (athlete's foot). More serious illnesses, such as Legionella pneumophila (Legionnaire's disease), may also spread through contaminated swimming pools and spas, as well as through contact of contaminated cooling water with air used in building ventilation systems.
Halogens, in particular chlorine and bromine, have traditionally been used to combat microbial contamination of swimming pools, hot tubs, spas, etc. As strong oxidizing agents, halogens are effective in destroying and preventing the growth of a wide variety of organisms. They can be utilized in a variety of forms, including chlorine gas, liquid chlorine, and more typically chlorine- or hypochlorite-releasing agents. Calcium hypochlorite, Ca(OCl).sub.2, is commonly used to treat public swimming pools, and contains 70% available chlorine. Chlorinated isocyanurates, including dichlor and trichlor and their salts, are commonly used to treat private swimming pools. Alternatively, chlorine can be generated by electrolysis for use in swimming pools. In combination with other measures designed to limit the build-up of organic matter in pool water, a constant adequate level of available chlorine of 1 to 3 ppm is generally required to maintain a pool in a pathogen-free state.
The use of chlorine, hypochlorite, and chlorine- and hypochlorite-generating water treatment chemicals (hereinafter referred to as "chlorine"), and in particular pool, hot tub, and spa treatment chemicals, presents numerous problems, however. Most notably, chlorine has been associated with health risks ranging from mild skin and eye irritation to an increased incidence of cancer. Chlorinated products, resulting from the reaction of chlorine with organic matter present in pool water, are thought to produce these adverse effects. In particular, chlorinated hydrocarbons, produced in pool water and then ingested by bathers, are suspected carcinogens.
Other disadvantages associated with the use of chlorine as a biocide relate to its performance and cost. The biocidal activity of chlorine is very sensitive to the environment in which it is used. Specifically, chlorine is only effective as a biocide within a narrow pH range. Relatively small variations in pH, therefore, can cause a loss of biocidal activity. Chlorine's sensitivity necessitates both careful monitoring of pool water pH as well as the adoption of pH-corrective measures to maintain the pH in a suitable range. Exposure to sunlight can also effect biocidal activity, as sunlight destroys hypochlorous acid formed from the hydrolysis of Cl.sub.2. This necessitates the addition of stabilizers to prevent the loss of biocidal activity from this source. The use of a strong oxidizing agent, such as chlorine, can also cause aesthetic problems, including bleaching and discoloration of swimwear, greenish hair, etc. In addition, the increasing cost of chlorine-based pool chemicals makes their use in large quantities less favorable economically.
For these and other reasons, it is desirable to reduce the quantity of chlorine needed and used to achieve an acceptably low level of microorganisms in swimming pools, hot tubs, spas, etc. A variety of compositions have been suggested for this purpose, including compositions containing heavy metal ions such as copper, silver, zinc, and nickel. Metal ions are known biocides, and have been provided as metal salt-based compositions for the treatment of swimming pools and other bodies of water. In particular, water soluble inorganic salts of copper, such as copper sulfate, copper nitrate, and copper chloride, have been suggested for use as algaecides and/or bactericides for the treatment of water.
The use of copper or copper ion sources, however, presents several disadvantages. Copper ions react with naturally occurring anions in alkaline or near-alkaline water, and precipitate as insoluble salts of, e.g., carbonate, oxide, and/or hydroxide. Copper precipitation is also sensitive to pH. Precipitation leads to a loss of biocidal activity as the copper ions are no longer available in solution. Precipitation also causes aesthetic problems including turbidity of water and the formation of stains on surfaces, such as pool surfaces. Conventional wisdom has been that, at copper levels sufficiently high to have a significant biocidal effect, it is necessary to add complexing agents having ligands that coordinate with the copper ion in order to shield the ion from the anions in solution thereby keeping it from precipitating and available for biocidal action. See U.S. Pat. No. 5,632,904. A variety of sequestering agents have been used to enhance the stability of the copper ions in solution in this way. For example, EDTA (ethylene diamine tetra acetic acid), citric acid, and salicylic acid are known to stabilize copper ions in solution by sequestering them. However, these sequestrants can be broken down in the presence of oxidizing agents such as chlorine, which will generally still be necessary in some quantities despite the use of metal biocides. In addition, sequestrants can bind metal ions so strongly that the biocidal activity of the ions is inhibited. These factors render the use of sequestrant-containing biocides complicated and difficult for the average pool user.
In addition, copper salt biocides are more effective against algae than against bacteria and other pathogens. In order to obtain significant bactericidal activity from copper salt biocides, unreasonably high copper concentrations are necessary. As a result, copper salt containing biocides are generally suitable as algaecides, requiring the use of additional biocides to control bacteria and other pathogens.
Preparation of copper-salt biocides, including copper-salt biocides containing salts of other metal ions, such as silver and zinc salts, has also proven problematic. Specifically, the failure to adhere to an ordered sequence of additions in the preparation of known copper, silver, and zinc biocides has produced uncontrollable frothing as well as the formation of black deposits during formation or compounding of the biocidal composition.
There is a need, therefore, to improve compositions of this type, and particularly, to provide metal biocide compositions for treating recirculating bodies of water that permit maintenance of the water in a pathogen-free and aesthetically acceptable state at reduced chlorine levels, while simultaneously reducing or eliminating the problems of staining and turbidity that have become associated with the use of metal biocides without the need for sequestrants, as discussed above.
It is, therefore, an object of the present invention to provide an improved metal salt-based composition for treating recirculated bodies of water to simultaneously inhibit microbial and algal growth and to reduce, as a result of the action of these combined metals, the amount of chlorine necessary to maintain the water in a pathogen-free and aesthetically acceptable state.
It is another object of the present invention to provide a metal salt-based composition for treating water that provides copper, zinc, and silver ions in solution, but maintains copper as well a silver at concentration levels below the levels that will result in staining of surfaces, such as pool surfaces, that contact the water, and also reduces or eliminates turbidity of the water, without requiring sequestration of the copper ions that are in solution.
It is a further object of the present invention to provide a composition that has a simple method of manufacture that eliminates the need for any special order of addition, as well as the need for heating and/or cooling steps or applying pressure and that does not result in frothing or black deposits forming during manufacture.
It is a further object of the present invention to produce a metal-salt based composition that quickly provides and effectively maintains concentrations of metal ions that reduce, control, limit, or inhibit the growth of microorganisms in water.
It is a further object of the present invention to provide a water treatment composition, a water treatment system containing the composition, and a method for using the composition that is characterized by ease of handling, simplicity of use, long lasting effects (in the sense that the biocidally active ions remain present and active in the water for several months), and effectiveness at producing clear, pathogen-free water in swimming pools, hot tubs, spas, fountains, ponds, humidifiers, cooling systems, and any other applications when microbial contaminants (e.g., bacteria, algae, fungi, viruses, etc.) are problems.
It is a further object of the present invention to provide a solid metal salt-based water treatment composition that can be easily solidified without expansion or shrinkage, and that can be easily molded into different shapes, such as tablets, sticks, or pellets, or stuffed into various holders, such as tubes.
It is a further object of the present invention to provide a metal salt based water treatment composition that reduces or eliminates the need for commonly used added metal ion sequestrants in the water (such as EDTA, citric acid, or high levels of ionic polymers, etc.), while avoiding staining of the surfaces in contact with the water, and turbidity of the water.
These and other objects and advantages, as well as the nature and proper use of the invention, will be readily apparent to those skilled in the art from the following description and claims.